1. Field of the Invention
The present invention relates to a star-shaped oligothiophene-arylene derivative and an organic thin film transistor using the derivative. More particularly, the present invention relates to a star-shaped oligothiophene-arylene derivative in which an oligothiophene having p-type semiconductor characteristics is bonded to an arylene having n-type semiconductor characteristics positioned in the central moiety of the molecule and forms a star shape with the arylene, thereby simultaneously exhibiting both p-type and n-type semiconductor characteristics.
2. Description of the Related Art
General organic thin film transistors (OTFTs) comprise a substrate, a gate electrode, an insulating layer, source/drain electrodes, and a channel layer. Organic thin film transistors are classified into bottom-contact (BC) OTFTs wherein a channel layer is formed on source and drain electrodes, and top-contact (TC) OTFTs wherein metal electrodes are formed on a channel layer by mask deposition.
Inorganic semiconductor materials, such as silicon (Si), have been commonly used as materials for channel layers of OTFTs. However, since the preparation of such inorganic semiconductor materials involves high costs and requires a high-temperature vacuum process to fabricate OTFTs, organic semiconductor materials are currently replacing inorganic semiconductor materials in order to fabricate large area, flexible displays at reduced costs.
Recently, studies on organic semiconductor materials for channel layers of OTFTs have been actively undertaken and the characteristics of the devices have been reported. Of these, a great deal of research is currently concentrated on low molecular weight materials and oligomers, e.g., melocyanines, phthalocyanines, perylenes, pentacenes, C60, thiophene oligomers, and the like. Lucent Technologies Inc. and 3M Inc. developed devices with charge carrier mobilities as high as 3.2-5.0 cm2/Vs using a pentacene single crystal (Mat Res. Soc. Symp. Proc. 2003, Vol. 771, L6.5.1-L6.5.11). In addition, CNRS, France, reported a device having a relatively high charge carrier mobility of 0.01-0.1 cm2/Vs and a relatively high on/off current ratio (Ion/Ioff ratio) using an oligothiophene derivative (J. Am. Chem. Soc., 1993, Vol. 115, pp. 8716-9721).
However, since the prior art devices are largely dependent on vacuum processes for thin film formation, the fabrication of the devices incurs considerable costs.
On the other hand, high molecular weight-based organic thin film transistors (charge carrier mobility: 0.01-0.02 cm2/Vs) employing a polythiophene-based material (F8T2) have already been fabricated and tested (PCT Publication WO 00/79617, Science, 2000, vol. 290, pp. 2132-2126). U.S. Pat. No. 6,107,117 discloses the fabrication of an organic thin film transistor with a charge carrier mobility of 0.01-0.04 cm2/Vs by employing polythiophene P3HT, which is a representative regioregular polymer.
Since the regioregular polythiophene P3H5 shows a charge carrier mobility of about 0.01 cm2/Vs but a high off-state leakage current (10−9 A or more), leading to a low Ion/Ioff ratio of 400 or less, it is not applicable to the fabrication of electronic devices.
Low molecular weight organic semiconductor materials for organic thin film transistors that can be spin-coated at room temperature and simultaneously satisfy the requirements of high charge carrier mobility and low off-state leakage current, have not hitherto been reported.